Electromagnetic solenoid

ABSTRACT

An electromagnetic solenoid comprises a coil wound around a coil case and a plunger inserted into the coil so as to be slidable in the axial direction, wherein a tape impregnated with a thermosettable resin is wound on the trunk portion of the coil case and the coil is wound on the wound tape.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control valve of a type ofelectromagnetically proportional operation (an electromagnetic solenoid)used for an electronic-controlled power steering system (EPS) for a car.More particularly, it relates to an improvement in a coil bobbininstalled in the control valve.

2. Discussion of the Background

There has so far been known a device as shown in FIG. 1 which waspublished, for example, in Japanese Utility Model Publication No.35009/1982.

In FIG. 1, a reference numeral 1 designates a solenoid device, a numeral2 designates a solenoid coil, a numeral 3 designates a plunger (movableiron core) capable of sliding in the direction of the arrow mark, anumeral 4 designates a push rod fixed to the top end of the movable ironcore 3, a numeral 5 designates a valve body (an oil pressure valve body)connected to the front end of the solenoid device 1, a numeral 6designates a spool which is arranged in the valve body 5 and is moved inits axial direction of the valve body 5 by pressure caused by thesliding movement of the plunger 3, a numeral 7 designates a springbearing, a numeral 8 designates a spring and characters T, A and Pdesignate oil pressure flow paths.

The operation of the solenoid device having the construction asdescribed above will be illustrated.

When the solenoid coil 2 is actuated by current conduction from anexternal d.c. power source device, the movable iron core 3 is moved inthe direction of the arrow mark to push the push rod 4. A pressing forceof the push rod 4 is transmitted to the spool 6 and the spool 6 iscaused to slide on the left hand in FIG. 1, pressing the spring 8.During the sliding movement of the spool 6, the oil pressure flow pathsT, A and P are changed.

In the conventional device constructed as above-mentioned, sincepressure oil (working oil) is filled in a space receiving the plunger 3,the pressure oil is apt to leak out to enter into the solenoid coil 2.Further, the inner diameter part of the solenoid coil 2 shrinks due totension produced at the time of winding a coil thereby to causedifficulty in sliding movement of the plunger.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the disadvantageof the conventional device and to provide an electromagnetic solenoidcapable of prevention of the leakage of pressure oil and providingsmooth sliding movement of a plunger as well as improvement inair-tightness of the device and increasing reliability of the operation.

The present invention to provide an electromagnetic solenoid comprisinga coil wound around a coil case and a plunger inserted into the coil soas to be slidable in the axial direction, characterized in that a tapeimpregnated with thermosettable resin is wound about the trunk portionof the coil case and the coil is wound on the wound tape.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawing, wherein:

FIG. 1 is a cross-sectional view of a conventional solenoid device;

FIG. 2 is a cross-sectional view of the upper half portion of anembodiment of the electromagnetic solenoid according to the presentinvention; and

FIGS. 3 and 4 are respectively longitudinal cross-sectional views of animportant part of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described with referenceto drawing.

In FIGS. 2-4, a numeral 9 designates an electromagnetic solenoidattached at its front end part with a valve body (oil pressure controlvalve) though it is not shown in Figures, a numeral 10 designates aplunger (a movable iron core) of the electromagnetic solenoid 9, anumeral 11 designates a rod made of a non-magnetic substance firmlyconnected to the plunger 10. A spool part 11a is formed at the front endpart of the rod 11. A numeral 12 designates a solenoid case made of softsteel material, a numeral 13 designates a coil bobbin which isconstituted by a coil case 14 formed by molding a resinous material, atape 15 impregnated with a thermosettable resin wound around the trunkpart (cylinderical part) 14a of the coil case 14 and a coil 16 wound onthe thermosettable resin impregnation tape with a number of turns. Asthe thermosettable resin, epoxy series resin is preferably used to forma epoxy glass tape (a prepreg tape). For example, epoxy resin isimpregnated and coated at a thickness of 0.06 mm in and on a glass basedtape of 0.07 mm thick to form a tape having a thickness of 0.13 mm.After winding the coil 16 on the wound glass tape, the coil bobbin 13 issubjected to heating to melt and cure the thermosettable resin on thetape 15. Then, the thermosettable resin enters into the inner layers ofthe coil 16 to relax stress produced at the time of winding the coil 16.For example, even when oil temperature rises at about 120° C. to causeexpansion of the coil, there is, allowance of 0.06 mm for the coatinglayer which has entered into the inner layers of the coil, thus thestress due to the expansion of the coil is released. Further, the curedtape 15 on the coil case 14 in a layer form separates the inner layer ofthe coil 16 from the coil bobbin 13 whereby leakage of the pressure oilinto the coil 16 can be prevented even though a crack is produced in thetrunk part 14a of the coil case 14. A reference numeral 17 designates astationary iron core, a numeral 18 designates a screw rod for adjustingpressure of return spring, which is screw-engaged with the centralthrough hole 17a of the stationary iron core 17, a numeral 19 designatesa return spring extending between the front end part of the screw rod 18and the rear end part of the rod 11 to return the plunger 10. A numeral20 designates a boss fitted at the front end part of the solenoid case12 and is firmly attached to the oil pressure valve body (not shown).Numerals 21, 22 and 23 respectively designate o-rings which function toprevent leakage of the pressure oil at the side of the coil bobbin 13. Anumeral 24 designates a sleeve fitted to a front through hole 17b of thesolenoid case 12, a numeral 25 designates a groove (an oil pressurereleasing part) formed in the outer circumferential part of the plunger10 and the groove is formed in such a manner that the pressure oil isreleased from the groove 25 at the time of movement of the plunger. Thegroove (the oil pressure releasing part) 25 is formed by shaving theplunger 10 from the front end part to the rear end part in the axialdirection (moving direction) of the plunger 10. The oil pressurereleasing part 25 may be a through hole passing through the plunger 10in the axial direction (moving direction) of the plunger.

The operation of the device according to the present invention is thesame as that of the conventional device. However, since a tapeimpregnated with a thermosettable resin is wound on the trunk part of acoil case and a coil is wound on the resin impregnation tape, crack andshrinkage of the coil case 14 are not produced due to tension producedat the time of winding the coil and there is no risk of leakage of thepressure oil. Accordingly a reliable and smooth sliding operation of theplunger can be obtained with simple and economical structure. Further,air tightness of the device is improved and reliability of the operationis remarkably improved

I claim:
 1. An electromagnetic solenoid comprising:an annular coil casehaving a cylindrical part; a plunger positionable in said cylindricalpart for movement along a longitudinal axis of said cylindrical part; atape impregnated with a thermosettable resin would about a radiallyouter surface of said cylindrical part; and an electric coil wound onsaid cylindrical part and over said wound tape, whereby said electriccoil is separated from said cylindrical part by said wound tape, andwhereby said resin relaxes stresses produced in said coil during thewinding thereof.
 2. The electromagnetic solenoid according to claim 1,wherein said coil case is formed of a molded resinous material and saidtape is impregnated with a thermosettable resin, is heated and issolidified after said coil has been wound.
 3. The electromagneticsolenoid according to claim 1, including an oil pressure control valveconnected to said plunger.
 4. The electromagnetic solenoid according toclaim 1, wherein said thermosettable resin is epoxy series resin.
 5. Thesolenoid of claim 1, wherein said coil case is formed of an insulatingmaterial.